Noninvasive lithotripters for the extracorporeal disintegration or destruction of kidney stones are now well known. Basically, an ellipsoidal reflector is utilized which is cut off at one end. An ellipsoid has two focus points, and a spark gap is provided at the first focus point. The reflector is filled with water. In initial efforts, both the reflector and the patient were emersed in a rather large water bath. More recent efforts have provided the cut off end of the ellipsoidal reflector with a rubber-like diaphragm. Typically, the reflector is placed in vertical position beneath a patient who lies on his back on a table with a cutout. The reflector is positioned in the cutout with the rubber diaphragm pressed against the patient's back in the area of the kidney. The position of the reflector is manipulated relative to the patient so that the kidney stone or other bodily concretion lies at the second focus point of the reflector.
Electrical energy is discharged across the spark gap in the form of a repeating series of sparks. Each spark flashes a certain amount of the water into steam, and may also produce some disassociation of the hydrogen and oxygen making up the water. In any event, a shock wave is generated. This shock wave passes through the water in the reflector, and is focused by the walls of the reflector on the second focus point. The shock wave energy passes through the water in the reflector and through the human tissues, which are 80% or more water, and focuses on the kidney stone. A repeated series of such shock waves reduces the kidney stone to fragments which pass out of the body with the urine.
Prior art extracoporeal or noninvasive lithotripters have been positioned with the reflector oriented substantially vertically upwardly. Gases produced by the sparks rise within the water in the lithotripter, and tend to accumulate beneath the diaphragm. This reduces the transmission efficiency of the shock wave from the reflector into the body tissues, and to the kidney stone or other concretion. Various structures and processes have been evolved to remove or to minimize the effect of such gases in the water.
The water pressure in the prior art systems has generally been substantially above ambient air pressure so as to cause the diaphragm to balloon upwardly for conformity with the patient's body. Such water systems in the prior art have generally been more or less permanently connected with water supplies, and this has limited mobility of the lithotripter apparatus. Such water systems have generally been rather complicated.